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In a world with climate change and environmental pollution, modern Biology is concerned with organismic susceptibility. At the same time, policy and decision makers seek information about organismic susceptibility. Therefore, information about organismic susceptibility may have far-reaching implications to the entire biosphere that can extend to several forthcoming generations. Here, we review a sample of approximately 200 published peer-reviewed articles dealing with plant response to ground-level ozone to understand how the information about susceptibility is communicated. A fuzzy and often incorrect terminology was used to describe the responsiveness of plants to ozone. Susceptibility was classified too arbitrarily and this was reflected to the approximately 50 descriptive words that were used to characterize susceptibility. The classification of susceptibility was commonly based on calculated probability (p) value. This practice is inappropriate as p values do not provide any basis for effect or susceptibility magnitude. To bridge the gap between science and policy decision making, classification of susceptibility should be done using alternative approaches, such as effect size estimates in conjunction with multivariate ordination statistics., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Evaluations of ozone effects on vegetation across the globe over the last seven decades have mostly incorporated exposure levels that were multi-fold the preindustrial concentrations. As such, global risk assessments and derivation of critical levels for protecting plants and food supplies were based on extrapolation from high to low exposure levels. These were developed in an era when it was thought that stress biology is framed around a linear dose-response. However, it has recently emerged that stress biology commonly displays non-linear, hormetic processes. The current biological understanding highlights that the strategy of extrapolating from high to low exposure levels may lead to biased estimates. Here, we analyzed a diverse sample of published empirical data of approximately 500 stimulatory, hormetic-like dose-responses induced by ozone in plants. The median value of the maximum stimulatory responses induced by elevated ozone was 124%, and commonly <150%, of the background response (control), independently of species and response variable. The maximum stimulatory response to ozone was similar among types of response variables and major plant species. It was also similar among clades, between herbaceous and woody plants, between deciduous and evergreen trees, and between annual and perennial herbaceous plants. There were modest differences in the stimulatory response between genera and between families which may reflect different experimental designs and conditions among studies. The responses varied significantly upon type of exposure system, with open-top chambers (OTCs) underestimating the maximum stimulatory response compared to free-air ozone-concentration enrichment (FACE) systems. These findings suggest that plants show a generalized hormetic stimulation by ozone which is constrained within certain limits of biological plasticity, being highly generalizable, evolutionarily based, and maintained over ecological scales. They further highlight that non-linear responses should be taken into account when assessing the ozone effects on plants., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Ground-level ozone (O 3 ) concentrations have been elevating in the last century. While there has been a notable progress in understanding O 3 effects on vegetation, O 3 effects on ecological stoichiometry remain unclear, especially early in the oxidative stress. Ethyelenediurea (EDU) is a chemical compound widely applied in research projects as protectant of plants against O 3 injury, however its mode of action remains unclear. To investigate O 3 and EDU effects early in the stress, we sprayed willow (Salix sachalinensis) plants with 0, 200 or 400 mg EDU L -1 , and exposed them to either low ambient O 3 (AOZ) or elevated O 3 (EOZ) levels during the daytime, for about one month, in a free air O 3 controlled exposure (FACE); EDU treatment was repeated every nine days. We collected samples for analyses from basal, top, and shed leaves, before leaves develop visible O 3 symptoms. We found that O 3 altered the ecological stoichiometry, including impacts in nutrient resorption efficiency, early in the stress. The relation between P content and Fe content seemed to have a critical role in maintaining homeostasis in an effort to prevent O 3 -induced damage. Photosynthetic pigments and P content appeared to play an important role in EDU mode of action. This study provides novel insights on the stress biology which are of ecological and toxicological importance., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Increased mixing ratios of ground-level ozone (O 3 ) threaten individual plants, plant communities and ecosystems. In this sense, O 3 biomonitoring is of great interest. The O 3 -sensitive S156 and the O 3 -tolerant R123 genotypes of snap bean (Phaseolus vulgaris L.) have been proposed as a potential tool for active biomonitoring of ambient O 3 . In the present study, an O 3 biomonitoring was conducted, with the S156/R123 tool, along with a monitoring of O 3 and other environmental conditions in an urban area in Athens, Greece, during the growing seasons of 2012 and 2013. Plant yield was evaluated to assess the effectiveness of AOT40 in interpreting O 3 -induced phytotoxicity. Across the two genotypes, an approximately two times lower total number of pods - and consequently lower bulk mass of seeds - was found in 2012 than in 2013, although there was no significant difference in the final AOT40 between the two years. No significant differences were observed in the stomatal density or conductance between the two genotypes, whereas it was estimated that, in both genotypes, the abaxial leaf surface contributes 2.7 fold to O 3 intake in comparison to the adaxial one. By testing the role of ambient air temperature in outdoor plant environment chambers (OPECs), it was found that increased temperature limits mature pod formation and complicates interpretation of O 3 impacts in terms of S156/R123 yields ratios. This is the first study providing evidence for a hormetic response of plants to ambient air temperature. This study also points out the complexity of using yield as a measure of O 3 impact across different environments with the snap bean system, whereas visible foliar injury is more consistently related to O 3 effects., (Copyright © 2016 Elsevier B.V. All rights reserved.)

It is widely accepted that elevated levels of surface ozone (O 3 ) negatively affect plants. Ethylenediurea (EDU) is a synthetic substance which effectively protects plants against O 3 -caused phytotoxicity. Among other questions, the one still open is: which EDU application method is more appropriate for treating fast-growing tree species. The main aims of this study were: (i) to test if chronic exposure of Salix sachalinensis plants to 200-400mgEDUL -1 , the usually applied range for protection against O 3 phytotoxicity, is beneficial to plants; (ii) to evaluate the effects of chronic exposure to elevated O 3 on S. sachalinensis; (iii) to assess the efficacy of two methods (i.e. soil drench and foliar spray) of EDU application to plants; (iv) to investigate the appropriate concentration of EDU to protect against elevated O 3 -induced damage in S. sachalinensis; and (v) to compare the two methods of EDU application in terms of effectiveness and EDU consumption. Current-year cuttings grown in infertile soil free from organic matter were exposed either to low ambient O 3 (AOZ, 10-h≈28.3nmolmol -1 ) or to elevated O 3 (EOZ, 10-h≈65.8nmolmol -1 ) levels during daylight hours. Over the growing season, plants were treated every nine days with 200mL soil drench of 0, 200 or 400mgEDUL -1 or with foliar spray of 0, 200 or 400mgEDUL -1 (in two separate experiments). We found that EDU per se had no effects on plants exposed to AOZ. EOZ practically significantly injured S. sachalinensis plants, and the impact was indifferent between the experiments. EDU did not protect plants against EOZ impact when applied as soil drench but it did protect them when applied as 200-400mgL -1 foliar spray. We conclude that EDU may be more effective against O 3 phytotoxicity to fast-growing species when applied as a spray than when applied as a drench. Keymessage: Soil-drenched EDU was ineffective in protecting willow plants against O 3 -induced injury, whereas foliar-sprayed EDU was effective even at the concentration of 200mgL -1 ., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The antiozonant and research tool ethylene diurea (EDU) is widely studied as a phytoprotectant against the widespread pollutant ground-surface ozone. Although it has been extensively used, its potential toxicity in the absence of ozone is unknown and its mode of action is unclear. The purpose of this research was to toxicologically assess EDU and to further investigate its mode of action using Lemna minor L. as a model organism. Application of EDU concentrations greater than 593 mg L(-1) (practically 600 mg L(-1)) resulted in adverse inhibition of colony growth. As no-observed-toxic-effects concentration (NOEL) we recommend a concentration of 296 mg L(-1) (practically 300 mg L(-1)). A hormetic response was detected, i.e. stimulatory effects of low EDU concentrations, which may indicate overcompensation in response to disruption in homeostasis. Growth inhibition and suppressed biomass were associated with impacted chlorophyll a fluorescence (ΦPSII, qP and ETR). Furthermore, EDU increased mesophyll thickness, as indicated by frond succulence index. Applications of concentrations ≥593 mg L(-1) to uncontrolled environments should be avoided due to potential toxicity to sensitive organisms and the environment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)